Tubular cartons made from card, and the like, have been in use for many years. There are a variety of different ways of forming the sleeve of a tubular carton, and cartons produced by helically winding a strip of cardboard around a former have been in use for many years.
In order to make manufacture easier and cheaper, the carton sleeve has more recently been made from a flat blank that is rolled to form the sleeve.
European patent application number 0 007 539 A1 discloses a tubular carton sleeve made from an inner and outer layer of material, the inner layer being narrower than the outer layer, but both layers being the same length.
The inner layer is superimposed on the outer layer slightly off set of the outer layer, such that a proportion of the end of the inner layer protrudes past the end of the outer layer and a corresponding proportion of the outer layer protrudes past the other end of the inner layer.
The longitudinal edges of the outer layer are folded over the narrower inner layer, to provide a neat finish to the ends of the sleeve. The thus joined sheets are then rolled to form the sleeve. The protruding section of inner layer forms a tab which is secured to the inner surface of the protruding section of the outer layer, and thus the ends of the sheets are joined together to form the sleeve.
UK patent application number GB -A- 2 038 276 discloses an alternative means of joining the edges of a tubular carton sleeve.
The blank of GB -A- 2 038 276 is produced from a single layer of cardboard material, which is folded to provide a double layered wall of the sleeve. The fold line of the blank is slightly offset from the centre of the sheet, so that when the sheet is folded one end of the sheet protrudes past the other end of the sheet to form a tab.
The folded sheet is then rolled to form a tube and the tab overlaps the folded edge of the sheet to form a join. End closures are applied to each end of the sleeve using a conventional rim rolling method. However, when the end closures are attached to the ends of the sleeve the increased thickness of the tube in the region of the join causes the material to distort.
In order to overcome this problem, a notch is removed from the edge of the blank in the region of the join. Therefore, when the blank is rolled and joined there is the same thickness of material all the way round the end of the sleeve in the region of application of the end closure, an a corresponding sleeve and tubular carton.
It is an aim of preferred embodiments of the present invention to provide an alternative blank for forming a sleeve of a tubular carton, and a corresponding sleeve and tubular carton.